1. Field of the Invention
The present invention relates to a semiconductor memory circuit, a semiconductor memory module using the same, and an acoustic signal reproducing system, and more specifically to a semiconductor memory circuit composed of a ROM (read only memory), a semiconductor memory module enabling a plurality of memory modules to coupled to each other, and an acoustic signal reproducing system for a Hi-Fi (high fidelity) acoustic signal of a compact disc type.
2. Description of Related Art
A conventional semiconductor memory circuit composed of semiconductor memory devices, in particular a semiconductor memory circuit composed of ROM devices, can be divided into one in which the memory is accessed at random, and another in which the memory is accessed sequentially. In the former type in which the memory is accessed at random, it is necessary to supply an address signal so as to select one word from a number of words stored in memory.
For example, in order to select one word from 2.sup.16 words (=65,536 words), an address signal of a 16-bit length is necessary. In addition, if the number of words is increased, the length of the address signal correspondingly becomes large. In ordinary cases, the address signal is supplied in a parallel format in order to speed up the access operation. As a result, the number of address signal lines is increased with the increase in the number of words, namely, with the increase in the memory capacity. Therefore, an addition electronic circuit becomes necessary with the increase in the memory capacity. This imposes restrictions at the time of increasing the memory capacity or of determining the memory capacity. Furthermore, since individual memory devices have only relatively small memory capacity, such individual memory devices have to be combined to each other. This gives a further restriction in wiring or locating the address signal lines.
In the type in which the memory is accessed sequentially, since it is not necessary to supply the address signal for the purpose of selecting the word, a large memory capacity can be easily realized by using a number of semiconductor memory devices. In addition, the restriction at the time of determining the memory capacity is small. The memory circuit in which the memory is accessed sequentially, is now widely used in household electric appliances. In the case that the semiconductor memory circuit including a number of ROM devices as semiconductor memory devices, is used as a storing medium for a Hi-Fi acoustic signal and the like, a voluminous memory capacity is needed.
On the other hand, a conventional semiconductor memory module has such a structure that a plurality of semiconductor memory modules cannot be connected directly to each other, and are connected through an additional circuit such as a printed circuit board.
In addition, an acoustic reproducing system using the conventional semiconductor memory circuit are used for example in an audio response system of household electric appliances. However, since the absolute memory capacity is small, it is difficult to reproduce a high quality signal such as a Hi-Fi acoustic signal.
As mentioned above, the conventional semiconductor memory circuit has required the wiring of the address signal lines, which is one restriction at the time of increasing or determining the memory capacity. In addition, it is difficult to constitute a sequential access memory medium in which the memory access is sequentially performed.
The above mentioned conventional semiconductor memory module composed of the semiconductor memory circuit has been disadvantageous in which since a plurality of semiconductor memory modules are interconnected in a fixed order or arrangement by use of the printed circuit board, the sequential access memory medium cannot be freely constituted. In other words, it is not possible to freely connect an arbitrary number of conventional semiconductor memory modules in an arbitrary order.
The above mentioned conventional acoustic signal reproducing system using the semiconductor memory circuit has various disadvantages since electric means and mechanical means exists in a mixed condition. For example, there is a limit in vibration proof, endurance and reliability, and miniaturization and lightening are impossible. Therefore, this conventional acoustic signal reproducing system is not suitable to reproduction of the Hi-Fi acoustic signal because of the limited memory capacity.